On 10/20/2011 08:13 AM, Charles Polisher wrote: > Mon, Oct 10, 2011, Dennis Jacobfeuerborn wrote: > <snip /> >> The physical numbers are consistent and what I would expect to see from the >> sata drives. >> The guests are minimal centos 6 installations so after booting they have >> virtually no processes running that could influence the benchmarks in any >> significant way. The hosts system is installed on /dev/sda so /dev/sd(b|c) >> are not influenced by the host system either. >> The entire setup is arranged to make benchmarking mostly reliable. >> If there were minor temporary fluctuations I would blame some external >> process but differences of almost 100% that are consistent for the lifetime >> of the virtual machine do not fit such a scenario. > > Hi Dennis, > > Did you figure this out? > > I'd suggest running something like smartctl -t long to rule out > underlying issues with a drive. But that's what puzzles me. On the host side both drives behave exactly identical and as expected. It's only in the guests where things get strange. I now have created a second disk /dev/vdb with an image on the second drive in my first guest so that it has disk from both physical drives that I can test in the same VM. These are the results: seekmark: /dev/vda: 130 seeks/s /dev/vdb: 9615 seeks/s hdparm -t: /dev/vda: 95 MB/s /dev/vdb: 1691 MB/s Running iostat shows no I/O activity when running the tests for /dev/vdb which explains the insane numbers. The question is why I get such different results when both devices are defined exactly the same way? In the guest the drive are running using virtio with type=raw and cache=none. On the host the backing filesystems look exactly the same: [dennis at nexus ~]$ cat /proc/mounts|grep backup /dev/sdb3 /mnt/backup01 ext4 rw,seclabel,relatime,user_xattr,acl,barrier=1,data=ordered 0 0 /dev/sdc3 /mnt/backup02 ext4 rw,seclabel,relatime,user_xattr,acl,barrier=1,data=ordered 0 0 The drives are identical in every possible way: [dennis at nexus ~]$ sudo hdparm -i /dev/sdb /dev/sdb: Model=SAMSUNG HD103SJ, FwRev=1AJ100E5, SerialNo=S246J9JB801028 Config={ Fixed } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=16 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio1 pio2 pio3 pio4 DMA modes: mdma0 mdma1 mdma2 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 AdvancedPM=yes: disabled (255) WriteCache=enabled Drive conforms to: unknown: ATA/ATAPI-0,1,2,3,4,5,6,7 * signifies the current active mode [dennis at nexus ~]$ sudo hdparm -i /dev/sdc /dev/sdc: Model=SAMSUNG HD103SJ, FwRev=1AJ100E5, SerialNo=S246J9JB801029 Config={ Fixed } RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4 BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=16 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120} PIO modes: pio0 pio1 pio2 pio3 pio4 DMA modes: mdma0 mdma1 mdma2 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 AdvancedPM=yes: disabled (255) WriteCache=enabled Drive conforms to: unknown: ATA/ATAPI-0,1,2,3,4,5,6,7 * signifies the current active mode Regards, Dennis